Single‐Crystal Structure Determination and Solid‐State NMR Investigations of Lithium Nitridosilicate Li₂SiN₂ Synthesized by a Precursor Approach Employing Amorphous “Si(CN₂)₂”

Abstract

Amorphous silicon bis(carbodiimide) “Si(CN2)2” has been identified as a reactive precursor for the synthesis of nitridosilicates that is specifically useful in the temperature region below 1000 °C. In this context the applicability and reactivity of amorphous “Si(CN2)2” towards Li3N in comparison to silicon diimide Si(NH)2 has been studied using high‐temperature in situ powder diffraction and DSC measurements. During the current investigation single crystals of Li2SiN2 have been obtained and the crystal structure of this Li+ ion conductor has been determined and refined: [Pbca, no. 61, a = 9.907(2), b = 9.907(2), c = 15.014(3) Å, Z = 32, R1 = 0.038, 1460 data, 142 parameters]. In the solid, Li2SiN2 consists of two interpenetrating cristobalite type nets which are made up from hetero‐adamantane‐like [Si4N6]N4/2 groups. The eight crystallographically independent Li+ sites are ordered at room temp. and exhibit coordination numbers 3 to 5. The 7Li and 29Si solid‐state MAS NMR spectra of Li2SiN2 are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Nitridosilicates and Oxonitridosilicates: From Ceramic Materials to Structural and Functional Diversity

“…Short LiÀLi distances and coordination numbers 3 and 5 for Li + allowed possible Li + pathways to be considered for this material. [38] The structure of CaSiN 2 contains vertex-sharing [SiN 4 ] tetrahedra, as already mentioned above (see Figure 8). The tetrahedra are linked to form a three-dimensional stuffed cristobalite-type framework that is isostructural with that of KGaO 2 .…”

“…[5,39,166] The possibility of lithium ions to move effectively through silicon nitride frameworks renders these materials possible candidates for solid-state electrolytes in lithium batteries. [167] As mentioned above (Section 3), several lithium nitridosilicates have been reported (for example LiSi 2 N 3 , [36,37] Li 2 SiN 2 , [37][38][39] Li 5 SiN 3 , [5,40] Li 8 SiN 4 , [37,39] Li 18 Si 3 N 10 , and Li 21 Si 3 N 11 ). [39] Lithium ion conductivity has been observed and comprehensively studied for Li 2 SiN 2 (s(400 K) = 1.1 10 À3 W À1 cm À1 ) and [38] According to this assumption, the Li + ions could move in layers parallel to [001] (Figure 26).…”

Nitridosilicate und Oxonitridosilicate: von keramischen Materialien zu struktureller und funktioneller Diversität

“…B. LiSi 2 N 3 , [36,37] Li 2 SiN 2 , [37][38][39] Li 5 SiN 3 , [5,40] Li 8 [45] Ganz allgemein handelt es sich bei der Mehrzahl der bisher untersuchten Nitridosilicate um dreidimensional kondensierte Raumnetzsilicate, die durch Hochtemperaturreaktionen der entsprechenden Metalle und Siliciumnitrid oder Siliciumdiimid (Si(NH) 2 ) erhalten wurden. Infolgedessen ist das Spektrum an ketten-und schichtartigen Strukturen im Vergleich zu Oxosilicaten nach wie vor sehr begrenzt.…”

“…[167] Wie oben erwähnt (Abschnitt 3), wurden mehrere Lithiumnitridosilicate beschrieben (z. B. LiSi 2 N 3 , [36,37] Li 2 SiN 2 , [37][38][39] Li 5 SiN 3 , [5,40] Li 8 SiN 4 , [37,39] Li 18 Vor kurzem wurde ein neuartiger Syntheseweg für Lithiumnitridosilicate beschrieben, der die Verwendung von Lithium-Schmelzen zur Grundlage hat. [28] Dies führte zur Entdeckung einiger neuartiger Verbindungen, die vielversprechende Lithium-Ionenleiter darstellen kçnnten (z.…”

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

“…[9,10] In both compounds Li1 is coordinated by four N-atoms in distorted tetrahedral fashion (105-123°) with typical distances Li-N (values within the sum of the ionic radii). [9,11] The smaller lattice parameters of Li 4 Ca 3 Si 2 N 6 also lead to significantly 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 [12] It may be noted that the addition of 1 % of Eu to the reaction mixture yielded red single crystals, which, however showed no fluorescence under UV light at room temperature.…”